Noble gas isotopes that can be nuclear spin-polarized are very attractive imaging agents ,because of their high detection sensitivity for nuclear magnetic resonance. In particular, spin-polarized 3He enables fast, gas- space imaging of the lungs and airways for clinical diagnosis and physiological studies. Unfortunately, the limited availability of 3He severely limits the number of high-resolution lung imaging studies that can be performed. We propose to develop a system to recover and recycle the rare helium isotope so that high-resolution lung imaging can become common and inexpensive. The innovation is a cryogenic gas separation system that extracts and purifies the 3He from a patient's exhalation stream and saves it for re-polarization3 and reuse in other patients. In Phase I we will prove the feasibility of the He recovery system by (l) performing a proof-of-concept test that demonstrates the feasibility of efficiently separating, purifying, and sterilizing the 3He from exhalation gases, and (2) producing a conceptual design of a complete system to recover and recycle 3He. In Phase II we will build and demonstrate a complete recovery and recycling system. PROPOSED COMMERCIAL APPLICATIONS: Rare, noble gas isotopes are a potential breakthrough for medical imaging if they could be used economically. Uses for these isotopes include high- resolution, gas-space imaging of the lungs and airways, practical low-field MRI, studies of blood perfusion and brain physiology using soluble isotopes, and porous media studies based on diffusion of gaseous isotopes. Technology developed in this program will make these advances practical and economical by enabling these rare isotopes to be reused many times.